Early detection of breast cancer is critical to control the disease, but many women do not engage in breast cancer screening as often as recommended. Knowledge is lacking about what specific aspects of informational messages promote cancer screening behaviors most effectively, and about how informational messages are effective. The purposes of this study are to test the effects of theory-based messages, delivered by nurses, on women's intended use and actual use of mammography, clinical breast examination, and breast self-examination. Three message conditions will be compared: a) a no-message control condition, b) an informational message about recommendations for breast screening, and c) an informational message about recommendations and feelings, beliefs, and costs regarding screening. Whether the message effects are conditional on having facilitators (e.g., personal, affordable, and accessible health care) will be tested. Whether the message effect on mammography use is mediated through anxiety and beliefs about mammography will be examined also. In a longitudinal experimental design, two samples will be recruited: a population-based sample from drivers' licenses and Medicare lists and a sample from an urban hospital mammography clinic that serves women of color and low-income women. Eligible women will be those 51 and over who have not had a mammogram in the last year and who have not had cancer. Participants will be assigned randomly to intervention groups. Messages will be delivered by nurses via telephone and a mailed pamphlet (Time 1). Screening behaviors will be measured four months postintervention (Time 2), and one year after this follow-up (Time 3). Measures of intention to engage in screening in the next year and other study variables (anxiety, beliefs, and facilitators) regarding screening will be made at Time 2. Repeated measures analyses will be used to test the message effects on behavior and intention. Regressions will be used to examine the interrelationships among message effects, selected variables, and behaviors. Findings from this research could not only advance theoretical understanding of screening behavior, but also identify for nurses and other health practitioners the specific content of informational messages to improve breast cancer screening most effectively.